Sequence pulse starting circuit for fluorescent lamps



June 1, 1954 J. CAMPBELL 68 SEQUENCE PULSE STARTING CIRCUIT FORFLUORESCENT LAMPS Filed March 14, 1950 Fig 1. L

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Patented June 1, 1954 UNITED STATES PATENT OFFICE SEQUENCE PULSESTARTING CIRCUIT FOR. FLUORESCENT LAMPS John H. Campbell, Painesville,Ohio, assignor to General Electric Company, a corporation of New YorkApplication March 14, 1950, Serial No. 149,536 3 Claims. (Cl. 3.1596) l2 This invention relates generally to the starting In the drawing: andcontrol of electric discharge devices, such as Fig. 1 is a schematicdiagram or a starting-cirlow pressure positive column lamps of thefluocuit embodying my invention and illustrating rescent type, and moreparticularly to circuits the operation of two fluorescent lamps inseries suitable for use with fluorescent lamps-which refrom a direct oralternating curent source.

quire preheat of their thermionic cathodes at ig- 2 is a schematicd of oher 01 starting. cuit embodying my invention, modified to permit Myinvention is concerned with the series opthe use of thermal typeswitches rather than the eration of fluorescent lamps from a voltagesource, glow type illustrated in Fig. l.

of which the terminal voltag is insufficient to Referring to Fig. 1, thecircuit therein comstart a discharge by means of the usual inductiveprises a pair of fluorescent lamps I, l electrically surge switch-startcircuit, and is applicable to connected in series with each other andwith a both alternating and direct current circuits. ballast resistance2 across a pair of input termi- It is an object of my invention toprovide a new nals 3, 3 adapted to receive either alternating'or andimproved starting and operating arrangedirect current. The devices I, Iare positive colment for fluorescent lamps provided with at least umndischarge lamps compri n es en ially an one thermionic electrode, whicharrangement evacuated glass envelope containing a mixture of employs aminimum of equipment and assures argon at a pressure of a fewmillimeters along reliable starting, together with efflcient operation.with a small quantity of mercury. The electrodes Another object of myinvention is to provide 4, 5 and 4, 5' sealed into the ends of the lampan improved starting arrangement for fluoresmay consist of coils oftungsten Wire coated With cent lamps which allows the sum of the voltageactivated electron emitting materials such as drops across the lampsduring operation to b a, barium and strontium oxides. If desired, eachof high proportion of the line voltage, thereby in e devices y be acommercial W D suringahigh operating efiiciency. 5 sure fluorescent lampwherein the envelopeis One of the features of my invention is theprocoated internally with a suitable luminescent mavision, in thestarting circuit, of transforming terialhe a la t si t 2 pr f a y as ameans such asan ignition type pulse transformer, positive temperaturecoefiicient of resistance in of which a primary winding portion isconnected order to provide good current regulatin charin series with thedischarge circuit of a number acteristics and may, as illustrated,consist of an of fluorescent lamps. Asecondary winding-porincandescenttungsten fila nt amp.

tion of the pulse transformer is connected to, an ner f electrode 4 n pl i5 @011- auxiliary starting. electrode or capacitive plate nected, bymeans of a shunting circuit, to a ter associated with. each lamp. Thefilamentary minal of electrode 5. This shunting circuit comelectrodes inthe lamps are in series with a reprises aresistance 6 and a switch 1which maybe sistance and a switch device preferably of the of anysuitable type, either manually or autoglow or of the thermal type, inorder to allow prematically operable. For instance, I have illusheatingof the electrodes at starting. Such cirtrated a glow type switchcomprising a glass encuit connections may be extended to include anyveiope 8 ta n an a as such as n number of lamps, depending upon themagnitude and including therein a pair of electrodes i? and of thesupplyvoltage. In starting, whenever one It, electrode l8 consisting of acurved bimetal of the switches opens, a pulse is generated-by the liestrip. In its normal position, electrode 11 pulse transformer which isapplied to the .capacidoes not make contact with electrode It; howtiveplates of all the'lamps, including th lamp ever, when a suiiicientvoltage is applied across whose associated switch operated to producethe the glow tube, a discharge occurs therein which pulse. The lamp inquestion then starts and the heats up the electrodes and causes thecurved other switches successively open until all the end of electrodel8to bend over and make con- .lamps have started, a pulse beinggenerated at tact with electrode l7, whereupon the switch is the openingof any one switch to start its assoclosed and, a short-circuit beingformed, the glow ciated lamp. ceases. After a brief interval of time,the elec- For further objects and advantages-and for a trodes coolwhereupon they separat once more,

better understanding of my invention, attention and the circuit isopened. After lamp I starts, is now called to the following descriptionand to the voltage drop across it is less than the ionizing theaccompanying drawing. The features or my potential of thegas within theglow wi h. 'A invention believed to be novel willhe more-par-:cordingly, no glow occurs, the electrodes do not ticularlypointedoutinthe appendedclaims, become heated, and the switch stays permanentlyopened. Lamp I is provided with a similar shunting circuit comprising aresistor 6' and a glow switch I.

In accordance with my invention, I provide a pulse transformer 9 whichmay be a small ignition type autotransformer. The primary portion III oftransformer 9 is connected in series with the discharge circuit betweenthe terminals 3, 3' and the lamps I, I and the secondary portion I I isconnected to capacitive plates I2, I2 located approximately at themid-points of the glass envelopes of lamps I, I, respectively.

In operation, when line voltage is first applied to terminals 3, 3, theglow switches I, I operate and, after a brief interval, close, whichprovides circuit continuity through trodes of the lamps. The circuit atthis instant may be traced from terminal 3, through the tungsten lampballast 2, through primary portion it of transformer 9, throughelectrode 4, resistance 6, glow switch I, and electrode 5, then throughelectrode 4', ballast 6, glow switch I and electrode 5 back to terminal3'. The current flowing through the electrodes causes them to heat upand shortly thereafter switches I and I will have cooled sufiiciently toreopen. Since, due to normal tolerances in manufacturing, no twoswitches will be identical and open at exactly the same instant, it willbe assumed, for ease of explanation, that switch 1 opens first. Whenthis occurs, current is momentarily interrupted in the primary portionIll of autotransformer 9. The sudden interruption of current thereininduces a pulse of voltage in secondary portion I i which is applied bymeans of the capacitive plates I2 and I2 across the gaseous atmospherewithin the lamps I, I. This causes an ionization of the gas within thelamps and the arc strikes in lamp I. Lamp I' is not affected as yetsince its starting switch is still closed. When glow switch I opens, asecond pulse is generated in the same way and lamp I starts. Both theinductive surge due to the rupture of the primary circuit of transformer9, and the induced pulse in the secondary, are effective in striking thearc. The purpose of the resistances 6 and 6 in series with the contactsof each glow switch is to limit the preheat current to a value whichwill not cause an overvoltage condition across tungsten ballast lamp 2when the glow switches are closed. Under low voltage conditions, wherethe sum of the striking voltages of the two glow switches approaches oris greater than the line voltage, it may be desirable to shunt one ofthe switches by a resistance. Thus, placing a resistance 19 (shown indotted lines) in parallel with switch I, insures that switch I willstrike and start lamp I first, after which switch I will strike andstart lamp I. Although I have illustrated the arrangement as applied totwo lamps, it can obviously be applied to a greater number of lamps withensuing advantages and economy. Thus, only one pulse coil is requiredfor any number of lamps connected in series across a source. Theignition pulse coil, moreover, generates a high pulse voltage atstarting only, so that although the primary portion thereof must bedesigned to carry the discharge current, the secondary portion mayconsist of very fine wire since it carries only a negligible current,and that current only at the very instant of starting. Such transformerscan be made very small since the energy required to ionize the gas inthe lamps with a pulse applied through an external electrode isnegligible, being of the order of milliwatts.

the filamentary elec- Referring to Fig. 2, I have illustrated thereinanother embodiment of my invention which may be utilized to advantage inoperating fluorescent lamps from electrical circuits where the terminalvoltage is so low as to preclude the use of glow switches. Likereference numerals in this figure denote corresponding circuit elementsas in Fig. 1. In this circuit, I have substituted thermal type switchesI3 and I3 for the glow switches 1 and of Fig. 1. These switches arethermally associated with a small heating coil or resistance I4 which isinserted in series with the main discharge circuit. Switches I3 and I3comprise a pair of contacts and bimetallic members I5 and I5, which,upon being heated, bend away from their associated contacts, therebyopening their respective shunting circuits. The remainder of the circuitis in all other respects identical to that of Fig. 1.

The operation of this circuit is similar to that of Fig. l and differsonly in the following details: when voltage is initially applied toterminals 3, 3', the thermal switches being in their normally closedposition, current flows through the heating coil I4 and also through thefilamentary electrodes of the lamps I, I. The bimetallic members ofswitches I3, I3 heat up and open, the instant of the open circuitoccurring at slightly difierent times for each switch in normal course.When either of the switches opens, a pulse is generated which starts thedischarge in the lamp associated with that particular switch. When thelamps are lit, the discharge current which must flow through resistor I4keeps the thermal switches heated and accordingly opened. When the lampsare turned off, the switches gradually cool and, in due course, reclosethereupon assuming the position required for the next lightingoperation.

Referring to Fig. 3, the pulse coil therein illustrated shows an actualconstruction which I utihas to operate two -watt fluorescent lamps ofthe ordinary commercial variety from a 220-volt alternating currentcircuit. The dimensions of the coil are 2 length by diameter withprimary consisting of turns of No. 28 wire and secondary consisting of8000 turns of No. 41 wire. This coil demonstrates, in rather strikingfashion, the compactness and economy of equipment possible with myinvention. The ballast resistance 2 for this particular combinationconsists of a ZOO-watt, 1l5-volt tungsten filament lamp.

While certain specific embodiments have been shown and described, itwill, of course, be understood that various modifications may be madewithout departing from the invention. Thus, the circuit may equally wellbe used with lamps having but one thermionic electrode when operatedfrom a direct current source; or if two thermionic electrodes areprovided, one may be left unheated and the lamp subsequently turnedabout in its sockets when the first electrode has reached the end of itslife. Likewise, while a pulse coil wound as an autotransformer has beenillustrated as the transforming means, it is apparent that other wellknown equivalents may be utilized. The appended claims are, therefore,intended to cover any such modifications coming within the true spiritand scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Starting and operating apparatus for gaseous electric dischargedevices having therein spaced main electrodes at least one of which istherm ionic and adapted to be heated by the passage of currenttherethrough prior to the starting of said devices, comprising a andconnections from the outer end of said secondary portion to theauxiliary starting electrodes of said devices.

3. Starting and operating apparatus for low pressure d ischarge lampshaving spaced thermages, consequent upon the opening of said switches,to ionize each lamp in turn.

References UNITED STATES PATENTS Number Cited in the file of this patent

